1. Technical Field
The present invention relates to a thermoelectric material, and a thermoelectric module and thermoelectric apparatus comprising the same.
2. Description of the Related Art
In general, thermoelectric materials can be utilized in active cooling, waste heat power generation, and the like by using Peltier effect and Seebeck effect.
The Peltier effect occurs when a direct-current (DC) voltage is applied and boles of a p-type material and electrons of an n-type material are transported to allow for a heat generation and a heat absorption at both ends of the materials. The Seebeck effect occurs when heat is supplied from an external heat source and a current flow is generated through the material while electrons and holes are transported to generate a power.
Active cooling with these thermoelectric materials improves the thermal stability of devices, does not cause vibration and noise, and does not use a separate condenser and refrigerant. Therefore, the volume of these devices is small and the active cooling method is environmentally friendly. Thus, active cooling that uses such thermoelectric materials can be applied in refrigerant-free refrigerators, air conditioners, micro-cooling systems, and the like. In particular, when a thermoelectric device is attached to a memory device, the temperature of the device can be maintained in a uniform and stable state, as compared to conventional cooling methods. Thus, the memory devices can have improved performance.
In addition, when thermoelectric materials are used in thermoelectric power generation using the Seebeck effect, waste heat can be used as an energy source. Thus, thermoelectric materials can be applied in a variety of fields that increase energy efficiency or reuse waste heat, such as in vehicle engines and air exhausts, waste incinerators, waste heat in iron mills, power sources of medical devices in the human body powered using human body heat, and the like.
As a factor for determining the performance of such thermoelectric materials, a dimensionless performance index ZT defined as Equation 1 below is used:
                    ZT        =                                            S              2                        ⁢            σ            ⁢                                                  ⁢            T                    k                                    (        1        )            
where S is a Seebeck coefficient, σ is an electrical conductivity, T is an absolute temperature, and κ is a thermal conductivity.
To increase the performance of such thermoelectric materials, the values of the dimensionless performance index ZT should increase. Accordingly, there is a need to develop a material having a high Seebeck coefficient and electrical conductivity and low thermal conductivity.
It has been known in the art that if a low dimensional nanostructure is prepared by a process for implementing a high ZT value, the Seebeck coefficient is increased by a quantum confinement effect, and if an energy barrier having a thickness shorter than the mean free path of electrons and longer than the mean free path of phonons is formed in a thermoelectric semiconductor, since an electricity is passed therethrough and a heat is blocked, ZT values are increased.